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Oxide glasses pose high theoretical strength originating from their strong ionocovalent bonding, but they experience amplification of tensile stresses around defects under tensile loading and lack efficient stress dissipation mechanisms. Consequently, glasses exhibit low practical strength and fracture toughness, limiting the scope of their applications. Different strengthening and reinforcement approaches have thus been tested, but relatively little success has been achieved with respect to making the glasses intrinsically more ductile through composition optimization. Following earlier literature reports, a possible route to achieve this would be to prepare glasses with high Poisson's ratio above ~0.32. Yet, no oxide glasses with such high Poisson's ratio have been reported and the mechanical properties of oxide glasses with Poisson's ratio ≥ 0.30 are poorly understood. In this paper, we synthesize 25%La 2O 3–15%Al 2O 3–60%B 2O 3, 25%La 2O 3–15%Al 2O 3–60%SiO 2, and 25%La 2O 3–15%Al 2O 3–60%GeO 2 glasses (fractions in mol%), all exhibiting high Poisson's ratio values (~0.30). We evaluate the mechanical properties, including elastic moduli, Poisson's ratio, hardness, and resistance to indentation cracking of the as-prepared as well as densified glasses. In addition, the indentation deformation mechanism of the glasses along with the accompanying underlying structural changes is investigated. This study therefore presents insight into the composition-property relations of high Poisson's ratio glasses, which may be used in future design of ductile oxide glasses with potential applications in electronic devices, optical fibers, and load-bearing components of buildings or other constructions.